1. Field of the Invention
This invention relates to vacuum operated valve mechanisms, and more particularly to vacuum operated valve mechanisms for controlling transmission of fluid to servo means for emission control means.
2. Description of the Prior Art
Conventionally, various mechanisms have been proposed for reducing emissions from the vehicle engine, and more particularly various valve mechanisms have been proposed for controlling an air-fuel ratio and for reducing HC, NO and the like within the exhaust gas by means of introducing fresh air into the engine intake manifold. In general, highest vacuum will be produced within the intake manifold at the engine decelerating condition of vehicle. Thus, fuel such as gasoline adhered to the inside wall of the intake manifold will be sucked or transmitted to engine cylinders so as to increase the ratio of fuel to air. This results in the so-called after burn and in increasing of impure gas such as HC, NO. In order to reduce or eliminate the above drawbacks, the above valve mechanisms have been proposed to introduce fresh air.
However, it is required that the valve mechanisms are maintained in non-operating conditions when receiving the relative higher vacuum pressure during the engine idling condition. Thus, valve members of the valve mechanisms have been subjected to the strong biasing force of the spring. In prior valve mechanisms, therefore, there are drawbacks in that the valve members cannot operate so as to complete desired stroke or lift to assure momentary introduction of fresh air and a sufficient quantity of fresh air.